1. Field of the Invention
The present invention relates generally to heat exchangers and, more specifically, to a heat exchanger and method of assembly for an automotive vehicle.
2. Description of the Related Art
It is known to provide automotive vehicles with heat exchangers such as condensers, evaporators, heater cores and coolers. These heat exchangers are alternating rows of tubes or plates with convoluted fins made of a metal material such as aluminum or an aluminum alloy. Many of these heat exchangers have turbulators disposed within the tubes that require internal brazing. Previously, the tubes and turbulators have been brazed in a vacuum furnace. Recently, a process known as "controlled atmosphere (CAB)" furnace brazing has been used with non-corrosive fluxes. CAB furnace brazing has been preferred over vacuum furnace brazing due to improved production yields, lower furnace maintenance requirements and greater braze process robustness.
It is also known that the CAB furnace brazing currently used to manufacture aluminum heat exchangers requires the use of fluxing agents, either chloride based or fluoride based. The use of these fluxing agents with conventional aluminum heat exchangers promotes the dissociation and disruption of the native aluminum oxide and magnesium oxide layers present on the surface of the aluminum heat exchanger to promote wetting of the molten clad layer between mating components.
It is further known for CAB furnace brazing that an inert gas such as nitrogen gas is used to provide a non-oxidizing atmosphere. Although considered to be non-oxidizing, nitrogen gas contains residual impurities, most notably oxygen and water vapor. Although the aluminum heat exchanger is pre-cleaned using alkaline cleaning agents which reduce the native aluminum oxide layer, the surface of the aluminum heat exchanger will re-oxidize in the CAB furnace due to the presence of the oxygen and water vapor in the nitrogen gas. To minimize reoxidation of the aluminum heat exchanger during the brazing process, the oxygen and water vapor in the nitrogen gas may be purified to less than twenty parts per million (20 ppm).
Although CAB furnace brazing has worked well, it suffers from the disadvantage that the internal tube surfaces and the turbulator of the heat exchanger require individual fluxing before assembly and an overall fluxing of the completed assembly before brazing. Also, CAB furnace brazing suffers from the disadvantage that the individual fluxing of the components of the heat exchanger is costly and time consuming. Further, CAB furnace brazing suffers from the disadvantage that purified inert gas is not cost effective for use in high volume processing of aluminum heat exchangers.